Terminal differentiation of nail matrix keratinocytes involves up-regulation of DNase1L2 but is independent of caspase-14 expression

Terminal differentiation of keratinocytes in the epidermis and in epidermal appendages results in specialized forms of cell death. Keratinocytes of the nail matrix differentiate into nail corneocytes, the building blocks of the nail plate. Here, we show that, in contrast to the abrupt breakdown of the nucleus during corneocyte formation of epidermal keratinocytes, chromatin undergoes progressive condensation over several nail matrix cell layers below the transition zone to the nail plate, where nuclear DNA disappears. Virtually all keratinocytes in the cell layer immediately beneath the nail plate contained terminal deoxynucleotidyl transferase-mediated fluorescein-dUTP nick end labeling-positive DNA fragments. Nail matrix keratinocytes lacked processed caspase-3, a marker of apoptosis, and did not express caspase-14, a protease up-regulated during terminal differentiation of epidermal keratinocytes. By contrast, DNase1L2, which is also up-regulated during the differentiation of epidermal keratinocytes and plays an essential role in differentiation-associated degradation of nuclear DNA in epidermal keratinocytes, was strongly expressed in the nail matrix-nail plate transition layer. Our results show that caspase-14 is not strictly, if at all, required for differentiation-associated keratinocyte cell death and implicates DNase1L2 in terminal differentiation of nail matrix keratinocytes.

Learning from nudity: lessons from the nude phenotype

In mice, rats, and humans, loss of function of Foxn1, a member of the winged helix/forkhead family of transcription factors, leads to macroscopic nudity and an inborn dysgenesis of the thymus. Nude (Foxn1(nu)/Foxn1(nu)) mice develop largely normal hair follicles and produce hair shafts. However, presumably because of a lack of certain hair keratins, the hair shafts that are generated twist and coil in the hair follicle infundibulum, which becomes dilated. Since hair shafts fail to penetrate the epidermis, macroscopic nudity results and generates the - grossly misleading - impression that nude mice are hairless. Here, we provide an overview of what is known on the role of Foxn1 in mammalian skin biology, its expression patterns in the hair follicle, its influence on hair follicle function, and onychocyte differentiation. We focus on the mechanisms and signaling pathways by which Foxn1 modulates keratinocyte differentiation in the hair follicle and nail apparatus and summarize the current knowledge on the molecular and functional consequences of a loss of function of the Foxn1 protein in skin. Foxn1 target genes, gene regulation of Foxn, and pharmacological manipulation of the nude phenotype (e.g. by cyclosporine A, KGF, and vitamin D3) are discussed, and important open questions as well as promising research strategies in Foxn1 biology are defined. Taken together, this review aims at delineating why enhanced research efforts in this comparatively neglected field of investigative dermatology promise important new insights into the controls of epithelial differentiation in mammalian skin.

Immunology of the Human Nail Apparatus: The Nail Matrix Is a Site of Relative Immune Privilege

The nail apparatus is constantly exposed to environmental damage. It requires effective immune responses to combat infection, while avoiding the loss of nail production and regeneration by autoaggressive immunity. By immunohistology, we define here previously unknown characteristics of the normal human nail immune system (NIS). Compared with other regions of nail epithelium, human leukocyte antigen (HLA)-A/B/C expression is prominently down regulated on both keratinocytes and melanocytes of the proximal nail matrix (PNM), whereas HLA-G(+) is upregulated here. Together with the expression of macrophage migration inhibitory factor in PNM, this may serve to inhibit an natural killer (NK) cell attack on major histocompatibility complex (MHC) class Ia-negative PNM. PNM also displays strong immunoreactivity for potent, locally generated immunosuppressants such as transforming growth factor-beta1, alpha-melanocyte stimulating hormone, insulin-like growth factor-1, and adrenocorticotropic hormone, exhibits unusually few CD1a(+), CD4(+), or CD8(+), NK, and mast cells. Finally, MHC class II and CD 209 expression on CD1a(+) cells in and around the PNM is reduced, indicating diminished antigen-presenting capacity. Thus, the NIS strikingly differs from the skin immune system, but shows intriguing similarities to the hair follicle immune system, including the establishment of an area of relative immune privilege in the PNM. This nail immune privilege may offer a relative safeguard against autoimmunity. But, the localized intraepithelial defect of innate and adaptive immunity in the PNM revealed here also may impede effective anti-infection defense.

Induction of hard keratin expression in non-nail-matrical keratinocytes by nail-matrical fibroblasts through epithelial-mesenchymal interactions

Epithelium in the nail matrix is different from that at other body sites, in terms of clinical and histological appearance. Hard keratins are exclusively expressed in the nail matrix and bed and the hair apparatus, and hard keratin is considered a differentiation marker of these sites. Whether the expression of hard keratin in non-nail-matrical keratinocytes could be induced by nail-matrical fibroblasts was examined. Skin equivalents were constructed in three ways; ventral keratinocytes (from the ventral side of the digit) were cocultured with ventral fibroblasts (group A), ventral keratinocytes were cocultured with nail-matrical fibroblasts (group B), and nail-matrical keratinocytes were cocultured with ventral fibroblasts (group C). Immunohistochemical examinations with anti-hard keratin antibody (HKN-7) revealed hard keratin expression in groups B and C. HKN-7-positive cells were distributed continuously in the entire epithelial strata or in the suprabasal layer in group B, whereas HKN-7-positive cells were distributed spottily in group C. This study indicates extrinsic hard keratin induction in non-nail-matrical keratinocytes by nail-matrical fibroblasts and suggests that non-nail-matrical epidermal grafts may be effective in the treatment of deepithelized nail injuries. In addition, it is possible that lost nails could be reconstructed with grafts of "tissue-engineered" nail equivalent.

Nail bed keratinocytes express an antigen of the carcinoembryonic antigen family

Using a panel of monoclonal and polyclonal antibodies raised against human carcinoembryonic antigen (CEA) and CEA-related molecules, we detected strong expression of an antigen, with immunoreactivity consistent with non-specific cross-reacting antigen (NCA) (CD66c), in all of 26 normal human nail specimens obtained from various fingers and toes. In longitudinal sections, strong and constant expression of the NCA-like antigen was seen on keratinocytes distributed in the upper epithelial cell layers of the nail bed, while in transverse sections the expression was limited to the major central portions of the nail bed, but only where longitudinal epidermal ridges were observed. In the hyponychium and the ventral aspect of the proximal nail fold, the expression was weak or lacking. No expression was seen in the nail matrix, the nail plate, or the dorsal aspect of the proximal nail fold. The same results were obtained for all of the 26 nails studied. This report is the first to demonstrate that an antigen of the CEA family, with NCA-like immunoreactivity, is expressed in a specific subpopulation of keratinocytes in the nail bed. The specific expression pattern suggests that the antigen may play a part in adhesion of the nail plate to the nail bed.

Keratin expression in the normal nail unit: markers of regional differentiation

Differentiation within the nail unit was examined using a range of antikeratin monoclonal antibodies including the recently described antibody LHTric-1, specific to the acidic hair-type keratin Ha1. Keratinocytes of the nail matrix, nail bed and the digit pulp were characterized by different patterns of keratin expression. Nail matrix was the sole site of expression of Ha1, which colocalized in suprabasal matrix epidermis with epidermal keratins K1 and K10. Small amounts of K17 were found at the apex of the matrix in some cases. K6 and K16 were found where the epidermal surface folds forwards to become the ventral aspect of the proximal nail fold. The nail bed was distinguished by the absence of hair-type keratin Ha1 and the absence of markers of cornified epidermis and mucosal differentiation K1/K10 and K4/K13, respectively, while K6, K16 and K17 were detected. The basal keratin conformation marker, LH6, was expressed suprabasally throughout the nail bed. This complement of keratins exists in the nail bed in the absence of notable proliferative activity, and suggests a state of minimally developed differentiation which may be afforded by the physical or biological properties of the overlying nail. Keratins, K6, K16 and K17 were all found in the digit pulp in limited amounts, possibly in association with the epidermal component of the eccrine duct. The simple epithelial keratins, K7, K8 and K18, were found in small amounts in the specimens from younger individuals, mainly in epibasal cells of the apex of the matrix and in putative Merkel cells.

Anatomic distribution of melanocytes in normal nail unit: an immunohistochemical investigation

Very few histologic reports describe normal melanocytes of the nail unit. Previous studies predominantly address the distal nail matrix melanocytes; we found no review of nail-bed melanocytes in the literature. The proximal nail matrix melanocytes are difficult to identify; the cells cannot be identified by L-DOPA staining. More recently, their scarcity was confirmed by immunohistochemistry with a large panel of antibodies directed against melanocytes. We wished to detect the proximal nail matrix dormant melanocytes and compare their density and distribution with that of the other melanocytes in the distal matrix and nail bed and to establish criteria of normality that may help clarify the pathologic features of benign nevoid melanonychia in the nails of whites. A panel of five monoclonal antibodies (MoAbs), including HMB45 and TRP1 directed against antigens localized in early melanosomal vesicles, was investigated in frozen sections of six nail specimens from whites. Both vertical and horizontal sections were assessed to determine the presence of dormant melanocytes. Results showed that the proximal nail matrix melanocytes were clearly identified with MoAbs HMB45 and tyrosinase-related protein-1 (TRP-1). By contrast, melanocytes stained by MoAb against tyrosinase and L-DOPA reaction were evident, especially in the distal matrix. With MoAb TRP-1, the epithelial sheets showed counts of approximately 217+/-84/mm2 in the proximal matrix and of 132+/-34/mm2 in the distal matrix; the nail bed counts were only 45+/-25/mm2. The split epithelial sheets had 103+/-17/mm2 L-DOPA-positive melanocytes in the distal third of the matrix, but only a few of them were detected in the proximal matrix and none were noted in the nail bed. We clearly identified proximal nail melanocytes using MoAb HMB45 and TRP1. The total number of matrix melanocytes can be estimated as approximately 217/mm2. In proximal matrix, the dormant melanocytes compartment was predominant. In the distal matrix, two compartments were identified: a functionally differentiated and a dormant compartment. Contrary to classical opinion, longitudinal melanonychia originates more frequently in the distal matrix, not secondary to the larger melanocyte density but because only the distal matrix contains an active melanin synthesis compartment. Furthermore, the superficial distribution of proximal nail melanocytes in vertical sections showed a histologic feature that may simulate the pagetoid pattern of melanoma in situ.

Cellular features of differentiation in the nail

Biochemical analysis indicated that the human nail plate contains two distinct types of keratin (skin-type and hair-type keratins), and several population of keratinocytes are thought to be associated with development of the nail. To elucidate the nature of the differentiation occurring in nail development, we examined the patterns of molecular markers relevant to the course of differentiation in the skin and hair in the nail matrix as well as in cultured nail cells. The nail matrix was characterized by the mutually exclusive localization of skin-type and hair-type markers, while in the apical matrix the localization of two groups of keratins partially overlapped. Double-label immunofluorescence showed the existence of unusual cells coexpressing both keratins, thereby indicating that the nail matrix consists of skin-type and hair-type and additionally intermediate-type differentiating cells. The cultured cells taken from the ventral matrix which develop under hair-type differentiation in vivo were found to express skin-type along with hair-type keratins, suggesting alteration of the pathway of differentiation in vitro. The cellular diversification as seen in in vitro cultured cells provides further insight into nail differentiation which is related to the multiple patterns of keratin expression that generate in the nail matrix.

Proliferative compartments in the normal nail unit

The main distinction between the germinal matrix and the nail bed is that the former is the origin of all or most of the nail plate and the latter provides an epithelial surface to which the emerging nail can adhere. It has been argued that the nail bed may contribute substance to the nail plate and it is likely that if this was the case, epithelial proliferation in the nail bed would match that in the germinal matrix by a proportion appropriate to its contribution. We have measured the labelling index (LI) in the three major anatomical sites of the nail unit using two antibodies to antigens expressed in cycling cells. Using Ki-67 (MIB-1) and proliferating cell nuclear antigen (PCNA) as markers of cell proliferation we have defined the LI in the germinal matrix (MIB-1: 22.1%, PCNA: 33%), nail bed (MIB-1: 0.75%, PCNA: 1%) and digit pulp (MIB-1: 16.8%, PCNA: 17.4%). This suggests a low degree of proliferation in normal nail bed consistent with a minimal or non-existent contribution to the nail plate. This may change in hyperkeratotic nail dystrophies, where the nail bed LI is raised (MIB-1: 31%, PCNA: 29%), illustrating how nail bed behaviour can alter with disease.

Quantification of regional matrix nail production

The relative nail producing capacity of different regions within the nail matrix has not been quantified. In order to do this, the number of nail plate cells in the dorsoventral axis of 12 human great toenails was counted at five sites in the longitudinal axis, and compared with direct measurements of nail plate thickness at the same sites. The mean number of nail cells in the nail plate reached a maximum at the lunula, with no further increase along the length of the nail bed. At the mid-point between the proximal tip of the germinal matrix and lunula, mean cell numbers achieved 81% of the value at the lunula. Mean nail thickness was only 90% of its maximum at the lunula, with a further significant increase (P = 0.02) between the lunula and end of the nail bed. These observations suggest that the proximal nail matrix is the main source of nail within the matrix. This is consistent with clinical experience where distal matrix surgery has a low potential for scarring in comparison with proximal matrix surgery. The additional finding of increased nail thickness, but not cell numbers, along the nail bed make it likely that cells within the nail plate change shape as they move distally.

Serial cultivation of human nail matrix cells under serum-free conditions

We have established serial cultures of human nail matrix cells (NMCs) under serum-free conditions. We cultured NMCs using two different methods depending upon the volume of nail matrix obtained. When a sufficient amount of nail matrix was obtained, they were minced and treated with 0.25% trypsin and 0.03% EDTA. The NMCs were transferred directly as a dispersed cell culture into KGM medium. Because a sufficient amount of matrix was rarely obtained, we developed a method by which NMCs were cultured primarily as implanted small matrices in Eagle's MEM (high Ca+ medium) supplemented with 15% fetal bovine serum for the first 4 to 5 days; during this time, the NMCs expanded from the matrices and formed colonies around them. NMCs then were cultured with KGM. In both methods, KGM medium supported the growth of NMCs without a biological feeder layer. These cells could be cultivated serially for at least seven passages. Half of the cells were positively stained with a monoclonal antibody against hair (hard) keratin which is expressed in nail matrix in vivo, indicating that the cells originated from the nail matrix. These methods will now permit investigations of nail matrix cells that previously were unfeasible because of the relative lack of cells and difficulties with propagation.

Characterization of nail matrix melanocytes with anti-PEP1, anti-PEP8, TMH-1, and HMB-45 antibodies

BACKGROUND

The normal nail matrix contains quiescent melanocytes with a peculiar arrangement and behavior.

OBJECTIVE

Our purpose was to identify nail matrix melanocytes with antibodies that recognize melanocytic cells in tissue sections.

METHODS

We used the polyclonal antibodies anti-PEP1 and anti-PEP8 and the monoclonal antibody TMH-1, which recognize melanocytic enzymes, and the monoclonal antibody HMB-45, which reacts with melanoma cells and fetal melanocytes, but not with normal adult melanocytes. Nail matrix specimens were obtained from longitudinal specimens of eight white patients with ingrown toenails. Specimens from normal adult forearm skin were used as controls.

RESULTS

All nail specimens gave similar results. Dendritic melanocytes were more numerous in the distal than in the proximal nail matrix. They were not restricted to the basal layer, but were also found in the suprabasal layers of the nail matrix epithelium. Melanocytes were seen both a single dendritic cells among the nail matrix keratinocytes and as small clusters that appeared irregularly distributed along the length of the nail matrix. Each cluster usually consisted of three to four cells.

CONCLUSION

Even if normally quiescent, nail matrix melanocytes possess the key enzymes responsible for the formation of melanin. The suprabasal location of nail matrix melanocytes may be a consequence of the distribution of adhesion molecules in the nail epithelium. In fact, in the nail matrix alpha 2, alpha 3, and beta 1 integrins are not only expressed on the basal, but also on the fourth to fifth suprabasal layers, with suprabasal expression gradually decreasing from distal to proximal matrix. The behavior of nail matrix keratinocytes may cause the peculiar arrangement and behavior of nail matrix melanocytes.

Variation of differentiation in nail and bovine hoof cells

Human nail plate contains two distinct types of keratins, skin-type and hair-type keratins. To elucidate that nature of the differentiation pathway of nail, we examined the expression of these keratins in human nail as well as in cultured cells taken from bovine hoof matrix. In this study we succeeded in showing that human nail matrix is characterized by the segregated localization of skin- and hair-type keratins except for the apical matrix in which both types of keratins are co-expressed. These results allow us to infer that some of the nail cells possibly divert the pattern of keratin expression during differentiation in vivo. Cultured cells taken from the ventral matrix of bovine hoof, which undergo the pathway of hair-type differentiation in vivo, expressed skin-type keratins together with hair-type keratins, thereby indicating that these cells develop into another pathway of differentiation (skin-type differentiation) from hair-type differentiation developed in vivo. These results provide us with a further insight into nail differentiation under which nail cells develop into multiple patterns of differentiation in vivo and in vitro.

Characterization of cultured nail matrix cells

BACKGROUND

Cultures of epidermal cells are commonly used to study skin biology and differentiation. Recently a method to culture nail matrix cells has been established.

OBJECTIVE

We report the biologic characteristics of nail matrix cells in vitro compared with those of epidermal keratinocytes.

METHODS

Human nail matrix cells were isolated and cultured in defined medium. Electron-microscopic examination, growth rate, integrin expression and keratin synthesis pattern were evaluated. In addition, the cells were cultured in serum-containing medium.

RESULTS

Nail matrix cells appear to be larger than human epidermal keratinocytes and, at the ultrastructural level, they contain a higher euchromatin/heterochromatin ratio and a lower nucleus/cytoplasm ratio and have a higher growth rate. The synthesis of "hard" keratins was detected at all calcium concentrations. Immunofluorescence analyses showed the expression of alpha 2, alpha 3, and alpha 6 integrin subunits. When cultured in serum-containing medium, nail matrix cells produced an outgrowth of epithelium and a spontaneous migration phenomenon associated with a tendency to stratify in a semilunar area that resembles the architecture of the nail matrix. The pluristratified epithelium showed characteristic markers of nail differentiation.

CONCLUSION

Culture of nail matrix cells may represent a useful model to study the biologic properties of nail structure, alterations in some nail diseases and the effects of drugs.

Merkel cells in ontogenesis of human nails

Digital skin of human fetuses is known to contain a particularly high concentration of Merkel cells. Using antibodies against the simple epithelial cytokeratins (CK) 18 and 20, which are sensitive and specific Merkel cell markers, we studied immunohistochemically the main adnexal structure of digital skin, the nail anlage, in human fetuses (9-22 weeks of gestation) for the presence of Merkel cells. As early as week 9 some clustered Merkel cells were detected in the early matrix primordium. In specimens of week 12-15, abundant Merkel cells were found in the nail anlagen, particularly in the epithelium of the proximal nail-fold and the dorsal and ventral side of the apex region. In contrast, Merkel cells were essentially absent from the epithelium of the ventral matrix (surface-near portion), lunula and nail bed. Correspondingly, in these region, the adjacent dermis contained hardly any nerve fibres, whereas such fibres, as detected by neurofilament antibodies, were quite numerous adjacent to the proximal nail-fold epithelium. At week 22, the Merkel cell number in the nail anlage had decreased, and in adult nail matrix such cells were very rare. No Merkel cells were found in the dermal tissue surrounding the nail anlage while finger-tip skin of week 15, and particularly of week 22, exhibited single Merkel cells in the upper dermis next to clusters of such cells in the glandular ridges. We also found that Merkel cells were negative for CK 17.(ABSTRACT TRUNCATED AT 250 WORDS)

Coexpression of keratins characteristic of skin and hair differentiation in nail cells

To further investigate the differentiation of nail, this study examined the composition and expression patterns of nail keratin by using monoclonal antibodies specific for keratins characteristic of skin or hair differentiation. Immunoblotting studies revealed that bovine hoof plate contains skin and hair differentiation-specific keratins, whereas immunofluorescence staining also showed that both keratins were present in the suprabasal cells in the bovine nail matrix. Skin differentiation-specific keratins were found to be expressed in the apical and dorsal nail matrices, whereas the hair differentiation-specific keratins were expressed mainly in the ventral nail matrix and partially in the apical and dorsal nail matrices. Moreover, the localization of the two types of keratins partially overlapped. Double-label immunofluorescence showed that unusual keratinocytes that co-express skin and hair differentiation-specific keratins exist in the nail matrix. These results indicate that the nail matrix consists of both skin-type and hair-type differentiating cells and, additionally, intermediate keratinocytes that may be progressing the pathways of both skin and hair differentiation.

Characterization of sciellin, a precursor to the cornified envelope of human keratinocytes

The cornified envelope, located beneath the plasma membrane of terminally differentiated keratinocytes, is formed as protein precursors are cross-linked by a membrane associated transglutaminase. This report characterizes a new precursor to the cornified envelope. A monoclonal antibody derived from mice immunized with cornified envelopes of human cultured keratinocytes stained the periphery of more differentiated cells in epidermis and other stratified squamous epithelia including hair and nails. The epitope was widely conserved among mammals as determined by immunohistochemical and Western analysis. Immunoelectron microscopy localized the epitope to the cell periphery in the upper stratum spinosum and granulosum of epidermis. In the hair follicle, the epitope was present in the internal root sheath and in the infundibulum, the innermost aspect of the external root sheath. The antibody recognized a protein of relative mobility (M(r)) 82,000, pI 7.8. The protein was a transglutaminase substrate as shown by a dansylcadaverine incorporation assay. Purified cornified envelopes absorbed the reactivity of the antibody to the partially purified protein and cleavage of envelopes by cyanogen bromide resulted in release of immunoreactive fragments. The protein was soluble only in denaturing buffers such as 8 M urea or 2% sodium dodecyl-sulfate (SDS). Partial solubility could be achieved in 50 mM TRIS pH 8.3 plus 0.3 M NaCl (high salt buffer); the presence of a reducing agent did not affect solubility. Extraction of cultured keratinocytes in 8 M urea and subsequent dialysis against 50 mM TRIS pH 8.3 buffer resulted in precipitation of the protein with the keratin filaments. Dialysis against high salt buffer prevented precipitation of the protein. The unique solubility properties of this protein suggest that it aggregates with itself and/or with keratin filaments. The possible role of the protein in cornified envelope assembly is discussed. We have named this protein Sciellin (from the old english "sciell" for shell).

Patterns of expression of trichocytic and epithelial cytokeratins in mammalian tissues. III. Hair and nail formation during human fetal development

Cells forming hair and nail material are characterized by the synthesis of members of a particular group of alpha-keratin polypeptides (trichocytic cytokeratins. "T cytokeratins") different from epithelial cytokeratins ("E cytokeratins"). As the precursor cells to trichocytes are derived from fetal epidermal keratinocytes expressing only E cytokeratins, we have studied the patterns of expression of both T and E cytokeratins in developing human hair-and nail-forming tissues of different fetal stages, by immunocytochemistry using antibodies specific for certain T or E cytokeratins and by two-dimensional gel electrophoresis and immunoblotting. In developing hair follicles up to the early bulbous-peg stage (weeks 12-15 of gestational age), only certain E but no T cytokeratins were identified. T cytokeratins were first detected in the late bulbous-peg stage (in week-14 scalp skin) in certain cells of the central part of the hair cone. In hair-producing follicles (weeks 18-25), the lower hair matrix cells were positive for certain E cytokeratins, whereas T cytokeratins appeared in the uppermost portion of the matrix and, most prominently, in the maturing trichocytes. From the late bulbous-peg stage on. E cytokeratin antibody Ks13.1 selectively decorated the inner root sheath. In finger nail "anlagen", T cytokeratins were detected first in week 12 and 13 fetuses, specifically in cells of the lunula region. In more-advanced stages of nail formation, expression of T cytokeratins extended not only to the upper layers of the ventral nail matrix but was also found, albeit more sparsely, in cells of the whole nail-bed epithelium. Throughout these developmental stages, coexpression of T and E cytokeratins was noted in certain cells, including E cytokeratin 19. While in earlier stages E cytokeratins 10/11, characteristic of epidermal-type cornification, were noted in different regions, including the superficial stratum of the nail bed epithelium, they were later restricted to the epithelium of the proximal nail fold. The results show that terminal trichocytic differentiation starts, both in ontogeny and during the steady growth of hairs and nails, in cells expressing E cytokeratins and that coexpression of E and T polypeptides occurs in both kinds of appendages. While in the hair follicle, the change to the exclusive synthesis of T cytokeratins appears to take place relatively abruptly and simply, the development of nail structures from the ventral nail matrix seems to be more gradual and is characterized by more-complex patterns of coexpression of both kinds of cytokeratins.

Nail disorders. A review

The nail is capable of only a limited number of pathologic responses. Some of these alterations, including idiopathic disorders, infections, tumors, and drug-induced reactions, are reviewed in the light of recent observations. Whenever possible, clinicopathologic correlation has been emphasized. Specific suggestions are made for diagnostic technics and treatment modalities.

Morphology of corneocytes from human nail plates

A technique is described which permits the isolation of individual corneocytes from the superficial layers of the human nail plates. Tesa-film D is used to strip off the cells. The tape is mounted on a glass slide, stained with a mixture of methylene blue and rhodamine B. The parameters were size (surface mu2), shape (regular, irregular), nuclear inclusions and trabeculae. Specimens were obtained from 3 groups of patients (finger- and toe nails): (1) 60 healthy subjects with normal nails, males and females, in 3 age-groups (babies, adults, aged); (2) 10 patients with fast growing nails with psoriasis vulgaris and psoriatic nail involvement; (3) 9 patients with slow growing nails with lichen planus with nail involvement including one patient with Zinser-Engman-Cole-syndrome (dyskeratosis congenita). The nail growth rate was determined with a dissecting microscope-technique. Corneocytes of the dorsal nail plates of normal nails are of irregular polyedrical shape, not nucleated and show distinct but irregular trabecular network. Within each age-group, corneocytes are of rather uniform size but increase significantly (p less than or equal to .001) with age (e.g., thumbin males: 597 vs. 920 vs. 1008 mu2). Accelerated nail plate growth results in smaller corneocytes, and slowed down nail plate growth in larger corneocytes. It is concluded that cell proliferation (and abnormal keratinization) has a measurable effect on the size of corneocytes from the nail plates.

The ultrastructure of the skin of human embryos. X. Merkel tactile cells in the finger and nail

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